Lab 6 - Molecular Geometry - Lab 6 M olecular Geometr y...

4/15/13Lab 6 - Molecular Geometrywww.webassign.net/ebooks/wsugencheml1/lab_6/manual.html1/8Contents>Lab 6 - Molecular GeometryLab 6 - Molecular GeometryPurposeATo explore some simple molecular structures.BTo explore the relationship between bond order and bond length.CTo explore resonance structures.Goals•To compare Lewis structures to three-dimensional models.•To visualize the three-dimensional structures of some common molecules.•To obtain bond angle, bond length, and hybridization data for molecules.•To rationalize differences in predicted and measured values.•To learn how to use computer modeling software.IntroductionThe chemical and physical properties of covalently bonded materials are related to the spatial arrangement ofthe atoms and other electrons not involved in the actual bond formation. There are many ways to depict thespatial arrangement in both two and three dimensions. A Lewis structureis a two-dimensional representation ofthe arrangement of the atoms, bonding electrons and non-bonding (lone pair) electrons in a covalent material. In a Lewis structure, the nucleus is represented by the atomic symbol with a line between the atoms in a bonddepicting each pair of shared bonding electrons in the structure. Non-bonding electrons around the atoms aredepicted as dots. The steps to building a Lewis structure representation of a molecule are shown below. TheLewis structure of the formate ion, CHO2-, will be used as an example.1Calculate the electrons required (ER)= the minimum number of electrons necessary to satisfy the octet rule forthe non-hydrogen atoms and the duet rule for hydrogen. For CHO2-, this would be (2 electrons × 1 hydrogen

This
preview
has intentionally blurred sections.
Sign up to view the full version.

4/15/13Lab 6 - Molecular Geometrywww.webassign.net/ebooks/wsugencheml1/lab_6/manual.html2/8atom) + (8 electrons × 3 non-hydrogen atoms) = 2 + 24 = 26 electrons required.2Calculate the number of available valence electrons (VE)= the total number of electrons available for themolecule. For example, in CHO2-, this would be (1 C atom × 4 electrons) + (1 H atom × 1 electron) + (2 Oatoms × 6 electrons) + (1 electron as the ion has a charge of -1) = 4 + 1 + 12 + 1 = 18 valence electrons. Note:For ions, the charge must be included in this by adding the charge on an anion or subtracting the charge on acation.3Calculate the Shared Pairs (SP)= the number of electrons to be shared in bonds. The SP is 1/2(ER - VE); forCHO2-, this would be 1/2(26 - 18) = 4 shared pairs or four bonds.4Lone Pairs (LP)= the number of electron pairs belonging to only one atom. The LP is 1/2(VE -(2 × SP)); for CHO2-, this would be 1/2(18 - (2 × 4)) = 5 lone pairs. Notice that VE = 2 × (SP + LP).5Place the first atom in the molecular formula as the central atom, surrounded by the other atoms in thecompound.Figure 16Draw bonds (shared pairs) from the central atom to each surrounding atom. The bonds are represented as lines;each line represents two electrons. The number of lines should be equal to the number of shared pairs calculatedin step 3, which in this case is four. Since hydrogen follows the duet rule, it only prefers one bond. The fourth

This is the end of the preview.
Sign up
to
access the rest of the document.